1. Field of the Invention
The present invention relates to mechanisms for mounting cam barrels, and more particularly to mechanisms for mounting cam barrels which are used to translate lenses in optical devices such as cameras and the like.
2. Background Art
Camera zoom lenses typically comprise a lens subgroup, or subgroups, mounted within a lens barrel for axial displacement during a zooming operation. A lens subgroup may comprise several lens elements mounted on a lens element mount. Cam barrels are frequently used as mechanisms for zooming lens subgroups. In accordance with current state-of-the-art practices, cam barrels are mounted on a fixed barrel with very tight tolerances between the inside diameter of the cam barrel and the outside diameter of the fixed barrel. By having the cam barrel and fixed barrel interface with minimal clearance, tilt control is provided to ensure that the motion of the cam barrel is purely rotational. In order to prevent the cam barrel from translating axially, a circumferential slot is usually formed in the cam barrel through which a pin of a tightly toleranced diameter extends from the fixed barrel. The pin provides a minimum clearance constraint with the straight slot in the cam barrel.
The tight tolerances at the cam barrel and the fixed barrel interface and the tight tolerances of the pin with respect to the cam barrel slot add considerable cost to the mechanism. Moreover, even when tight tolerances are maintained, there must necessarily be some clearance between the mating parts so that the barrels may move with respect to one another. This clearance results in a variability in the position of the lens group as dictated by the position of the cam slot.
Prior art approaches exemplified by U.S. Pat. Nos. 3,441,339; 4,307,951 and 5,052,782, incorporated herein by reference, are concerned with mounting lenses, such as zooming lenses, but do not suggest what is essentially a zero-clearance mounting configuration which would solve the problems of expense and misalignment associated with the current approach in which cam barrels are mounted on fixed barrels with minimal clearance.